1. Field of the Invention
This invention pertains generally to electric field generation.
2. Description of the Related Art
Electric-field sensor technology relates to applications such as electrostatic proximity sensing (EPS) for anti-aircraft projectile fuzing applications; unattended ground sensors (UGS) for detection, classification, and identification of helicopters and other aircraft; localization and tracking of aircraft and other airborne objects in flight; and other intelligence, surveillance, and reconnaissance (ISR) applications. Electric-field sensors have also been used to measure atmospheric E-fields for lightning research and safety during rocket launch operations.
As used herein, the term electric field (E-field) refers to a quasi-static field; that is, one in which the charge relaxation time is short compared to the period of the highest source frequency or any movement of the boundary conditions (source, cluttered environment, and sensor). In a quasi-static field, the charge is assumed to move with the boundary conditions, and the resulting electric currents are so small that the magnetic field can be neglected. The sensors described above may be referred to as E-field anomaly detectors, and are analogous to the more well known magnetic anomaly detectors that have been used since World War II to detect distortions in, or modulations of, an external magnetic field (typically the Earth's magnetic field).
Some electric-field sensors are ground-based; that is, the Earth (or the platform upon which the sensor is mounted) becomes the reference electrode. Other E-field sensors are electrically floating; they may be flying, or they may be suspended in such a way that they form a complete sensor by themselves. Some ground-based E-field sensors are flush-mounted, while others stand upright from their mounting surface. Some sensors are small, with dimensions on the order of millimeters or centimeters, while others are large, with dimensions on the order of meters. Some sensors respond to DC fields, while others only respond to electric fields in various frequency bands.
Such sensors have been designed for various applications. Some are designed for atmospheric field research, including thundercloud formation and lightning safety studies. Some are designed for detection of aircraft outdoors, while others are designed primarily to detect humans indoors. Many different kinds of electric-field sensors are used to detect and/or characterize power lines. All these sensors are different sizes and shapes, and have different functions, yet they all share a common need for reliable, accurate calibration and/or testing in repeatable, laboratory conditions.